Add Redis readiness verification (#3555)

[ManelCoutinhoSensei]

Pull Request check-list

Please make sure to review and check all of these items:

• Do tests and lints pass with this change?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Is there an example added to the examples folder (if applicable)?
• Was the change added to CHANGES file?

NOTE: these things are not required to open a PR and can be done
afterwards / while the PR is open.

Description of change

Fixes #3555 (specially the comment on that issue)

Please check if you'd rather run the tests with check_ready=True by default (I also tested that) and if you think that any other tests deserve a second version with this flag set.

[petyaslavova]

Hi @ManelCoutinhoSensei, thank you for your contribution! We’ll review your change soon.

[ManelCoutinhoSensei]

@petyaslavova you need to rerun the failed tests due to the test suit flakiness